Zinc deposit morphology

Ammonium chloride (NH4CI) displays possibilities that seem difficult to exploit. The NH4CI appears to provide a better zinc deposit morphology at a current density of 1,200 A/m. During small-scale tests, however, several small explosions were observed. The explosion risk could possibly be reduced by operation at a lower current density, but this defeats the purpose of operating at high current density. 

Study impact of BSA type used on zinc deposition morphology via electrochemical methods and molecular modelling... 

Significant improvements in ECALE deposit morphology and quality were reported as achieved by switching from a thin layer cell to a thick layer H-form cell, integrated in an automated deposition system [46]. Thin epitaxial films of zinc blende CdTe, CdSe, and CdS with predominate (111) orientations were grown. 

Cathode deposit morphology can also be affected by the presence of trace elements in solution. An SEM micrograph of a zinc deposit from a pure or unadulterated electrolyte and time duration of two minutes at 10 mA/cm2 is shown in Figure 3. When U0 parts per billion of antimony was added to this solution, and a similar electrodeposition cycle was performed, an approximate ten-fold increase in crystallite size was obtained (see Figure U). 

The kinetics of zinc deposition on Zn electrode from a concentrated ZnC T KCl electrolyte containing commercial long-chain polymer additives was investigated using impedance spectroscopy [218]. The additive modifies the deposit morphology by changing some specific rates of the electrode reaction surface steps (see Fig. 7). 

The same mechanism of zinc electrodeposition on the GC electrode was observed in sulfate, chloride, and acetate ion solutions [227]. The anions mainly affected the nucleation densities during zinc deposition, which resulted in a different surface morphology. The nucleation rate constant was the same in the chloride and sulfate solutions and was equal to 1.22 x 10 s h In the presence of acetate and chloride ions, the deposited zinc film tends to grow in a multilayered pattern, while in sulfate solution, the zinc deposition forms irregular grains. A new approach to the estimation of zinc electrocrystallization parameters on the GC electrode from acetate solutions was described by Yu et al. [228]. 

Raeissi et al. [236, 237] showed that temperature, pH, and current density affected the morphology and texture, as well as the nucleation mechanism of the zinc deposits on carbon steel electrode. 

Fig. 8 Surface morphology of zinc deposits from (a) the gelatin-free solution 0.5 M ZnCb + 2 M HCl and (b) gelatin-containing solution 0.75 M ZnCl2 + 1.5 M HCl [380].

Traditionally, glues [362, 381-383] and arable gum [384] were used as organic additives in the electrowinning of zinc. Hosny [385] and Karavasteva et al. [386, 387] used surfactants to improve the deposit morphology and current efficiency. 

The peaks in particle incorporation often55 56,77,85,89 occur at the same current density as kinks in the polarization curve for metal deposition. For Au-Ai203 composite deposition77 the peaks and kinks also correlate with the preferred orientation of the Au crystallites. Similarly, for zinc-polystyrene composites54,76 the peak in polystyrene codeposition corresponds to a change in morphology of the zinc deposit. Polarization... 

Figure 14. Growth morphologies of zinc deposits (a) intermediate type, (b) basal type, (c) vertical type Black spots represent particles.

The main result of a more detailed investigation of Zn electrodeposition is that when intense hydrogen bubbling occurs at high potential or current density, the morphology of the ramified zinc deposit changes from dense-branching to fem-shaped dendrite [21]. The fern-shaped dendrite... 

Figure 2 - Effect of the Frame on the Morphology of the Zinc Deposit. A) Cathode and Anode Frame Opening are the Same Size, B) Cathode is Slightly Larger than the Anode Frame Opening, and C) Cathode is Much Larger than the Anode Frame Opening...

In the zinc/chlorine cell, the chlorine is stored as chlorine hydrate, Cl2 xH20 (x = 6—10), which precipitates as a solid below 9.6°C. During charge the electrolyte, aqueous zinc chloride, is cooled in a reservoir, while during discharge the reservoir is heated under controlled conditions. The cell itself, however, can be simple the electrodes are graphite and can operate without catalyst and the cell can be constructed from PVC without a separator. There remain some problems with the morphology of zinc deposits. 

Karavasteva M (2005) Kinetics and deposit morphology of copper cementation onto zinc, iron and aluminium. Hydrometallurgy 76 149... 

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